I've done some testing of the differences between the two difficulties (first option in the options menu, defaults to Normal, can be flipped to Easy).

Here's what's different on Normal that's notable to a speedrun:

• Most normal enemies have more HP. The generic trash still dies to 1 rocket or rider kick, but other things may need 2 hits; things that needed 2 now need 3.
• Most bosses take more hits the kill. The is most noticeable with midbosses and phase 1 of multi-phase bosses. The final boss phase of the stage has less of a boost, or none at all.
• Your energy regen is cut about in half during mech fights. It's no longer possible to finish fights with a flurry of offense; most mech fights require playing defensive to recharge.
• The final mech fight does not refill your health between phases, which is actually kind of a big deal coupled with the energy regen penalty above.

The last two points are the most important. While most of my mech fight strategies will still work, you'd have to spend time defending to recharge between offensive flurries; a LONG time recharging on the final fight. I wouldn't be surprised if this adds 3 minutes to the run on its own.

Of secondary importance are the other two points. More enemy HP means more backboosts while trying to rider kick through enemies, that's about all. More boss HP makes bosses take longer because at no time are you in danger during boss fights; it's just more time for no difficulty or style gain.

In general, Normal difficulty is "the same but takes longer". I personally feel Easy makes a cooler looking run even if you execute optimally in both difficulties. However, these differences make comparing runs between difficulties unfair.

For now I've added a difficulty field to the leaderboard so it's clearer. If someone besides me takes up running the game I'm more than willing to split the board into two categories.

Just noting this all for the record if anyone gets curious.